A hydraulic transmission such as that disclosed in Japanese Laid-Open Patent Application No. 2005-282830 is commonly provided as a transmission for a wheel loader or another industrial vehicle. This type of transmission has a torque converter disposed between the engine and the transmission body. Disposed inside the transmission body are a hydraulic clutch for forward travel and a hydraulic clutch for reverse travel whereby a switch is made between forward and reverse travel, as well as hydraulic clutches for a plurality of speed-change steps that can operate in forward and reverse.
With such a transmission, the hydraulic clutch for forward travel is engaged (brought into a power transmission state) and the hydraulic clutch for reverse travel is disengaged (brought into a power cutoff state) during forward travel, after which the hydraulic clutch of the corresponding speed-change step is engaged so that a suitable speed-change step is selected in accordance with the travel state or the like. Conversely, the hydraulic clutch for forward travel is disengaged and the hydraulic clutch for reverse travel is engaged during reverse travel, after which the hydraulic clutch of the corresponding speed-change step is engaged so that a suitable speed-change step is selected in accordance with the travel state or the like.
In a passenger vehicle, on the other hand, a twin-clutch transmission for a vehicle is provided for rapidly switching speeds (e.g., Japanese Laid-Open Patent Application No. 2001-99246). The transmission shown in Japanese Laid-Open Patent Application No. 2001-99246 has a first transmission mechanism for odd-numbered speeds, a second transmission mechanism for even-numbered speeds, and first and second clutch mechanisms provided in correspondence to the respective transmission mechanisms.
In such a configuration, it is possible to rapidly change speed from an odd-numbered speed-change step to an even-numbered speed-change step because the speed change can be prepared (pre-shifted) in the second transmission mechanism for even-numbered speeds when the vehicle is travelling in an odd-numbered speed, for example.